全文获取类型
收费全文 | 17372篇 |
免费 | 1599篇 |
国内免费 | 1161篇 |
专业分类
电工技术 | 617篇 |
技术理论 | 3篇 |
综合类 | 935篇 |
化学工业 | 6226篇 |
金属工艺 | 1385篇 |
机械仪表 | 577篇 |
建筑科学 | 466篇 |
矿业工程 | 263篇 |
能源动力 | 492篇 |
轻工业 | 1031篇 |
水利工程 | 93篇 |
石油天然气 | 1304篇 |
武器工业 | 168篇 |
无线电 | 1952篇 |
一般工业技术 | 1456篇 |
冶金工业 | 841篇 |
原子能技术 | 440篇 |
自动化技术 | 1883篇 |
出版年
2024年 | 114篇 |
2023年 | 428篇 |
2022年 | 979篇 |
2021年 | 1073篇 |
2020年 | 824篇 |
2019年 | 503篇 |
2018年 | 414篇 |
2017年 | 518篇 |
2016年 | 616篇 |
2015年 | 636篇 |
2014年 | 861篇 |
2013年 | 1007篇 |
2012年 | 942篇 |
2011年 | 1310篇 |
2010年 | 876篇 |
2009年 | 1016篇 |
2008年 | 922篇 |
2007年 | 995篇 |
2006年 | 937篇 |
2005年 | 761篇 |
2004年 | 585篇 |
2003年 | 537篇 |
2002年 | 480篇 |
2001年 | 470篇 |
2000年 | 405篇 |
1999年 | 362篇 |
1998年 | 270篇 |
1997年 | 226篇 |
1996年 | 187篇 |
1995年 | 170篇 |
1994年 | 139篇 |
1993年 | 122篇 |
1992年 | 110篇 |
1991年 | 75篇 |
1990年 | 67篇 |
1989年 | 26篇 |
1988年 | 25篇 |
1987年 | 29篇 |
1986年 | 15篇 |
1985年 | 20篇 |
1984年 | 17篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1974年 | 4篇 |
1959年 | 4篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
992.
L. Melo G. Giannetto L. Cardozo A. Llanos L. García P. Magnoux M. Guisnet F. Alvarez 《Catalysis Letters》1999,60(4):217-222
Acetone transformation into methyl isobutyl ketone (MIBK) was studied using a fixed-bed dynamic reactor at 160°C, 1 atm pressure
and acetone/H2 molar ratio=3. The reaction was carried out over Pt/HMFI bifunctional catalysts, with 0.30 wt% of platinum which was supported
over three aluminosilicates (Si/Al ratio=40, 95 and 160) and a borosilicate (Si/B ratio=44) with similar dispersion. The results
show that catalytic properties depend greatly on density and strength of the acidic sites of the catalysts. Moreover, the
limiting step of the MIBK synthesis reaction (aldolization of two acetone molecules) is carried out over the acidic sites
of the aluminosilicates, but not over those of the borosilicate, which considerably affects reaction selectivity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
993.
994.
995.
Kinetic analysis of non-enzymatic browning in carrot juice concentrate during storage 总被引:1,自引:1,他引:1
Hou-yin Wang Xiao-song Hu Fang Chen Ji-hong Wu Zheng-hua Zhang Xiao-jun Liao Zheng-fu Wang 《European Food Research and Technology》2006,223(2):282-289
The effect of storage temperature, storage time and total soluble solid (TSS) on the total sugar (TS), sucrose, glucose, fructose, total amino acid (TAA), pH, 5-hydroxymethylfurfural (HMF) and browning degree (BD) in carrot juice concentrate (CJC) stored at −18, 0, 25 and 37 °C was studied and the relationship between HMF and BD was established. Higher temperature at 25 and 37 °C had a significant effect (p<0.05) on TS, sucrose, glucose, fructose, TAA, pH, HMF and BD, while lower temperature at 0 and −18 °C had less effect, and the storage time and the soluble solid of CJC stored at 25 and 37 °C also had a significant effect on HMF formation and BD. At 25 and 37 °C, the formation of HMF and BD followed a first-order reaction well as a function of storage time; a good correlation between HMF formation and BD occurred. The formation of HMF could described by the total soluble solid value [TSS] and the BD value ([BD], absorbance at 420 nm) of CJC, the equation was [HMF] (content of HMF) = 1.2177 − 0.1124 × [TSS] + (2.835 + 0.3477 × [TSS]) × [BD] and [HMF] = 1.5510 − 0.4813 × [TSS] + (23.8847 + 0.7249 × [TSS]) × [BD] at 25 and 37 °C, respectively. 相似文献
996.
本研究采用热重分析法研究了分子筛ZSM-5填充海藻酸钠在空气中的热分解过程,升温速率分别为5K/min、10K/min、15K/min、20K/min和30K/min,温度范围为室温(298K)至1250K,并利用TGA曲线分析了复合材料的热分解特性。热重分析结果显示,热分解反应最剧烈的温度介于450~650K之间,热分解动力学分析表明,该热分解过程为一级反应,可通过最大失重速率温度法和Ozawa等失重率法分别计算求得活化能和频率因子。结果表明,活化能和频率因子随着失重率的增加而增大,分子筛ZSM-5的加入有利于海藻酸钠的热分解。 相似文献
997.
998.
为解决PROTOS M5卷接机组梗签输送装置中输送管道容易堵塞问题,通过Solid Works建立管道模型,利用Fluent分析软件模拟空气在管道中流动的形态,对流体在管道中的压力和流线进行分析,得到梗签输送管道的堵塞原因并对该装置进行了优化设计:将封闭式弯管改为开放式振槽,缩短输送管道长度;增加切碎梗签功能,将较长梗签切断,避免过长梗签卡在管道弯曲处;采用直管连接梗签箱与集中负压源,减少负压损失。结果表明:1管道在最大弯曲处、同一截面上出现螺旋式流动时,或在最大弯曲处出现流速为零时,以及管道压力损失过大时,均容易造成管道堵塞。2改进后管道压力和流线分布均匀,管道压力损失由452.8 Pa减小到245.5 Pa,有效解决了梗签输送管道堵塞问题。 相似文献
999.
Stephen L. Pahl David M. Lewis Feng Chen Keith D. King 《Journal of Bioscience and Bioengineering》2010,109(3):235-239
To investigate the nutritional value of the diatom Cyclotella cryptica (Reimann, Lewin, and Guillard) as an alternative feed for use in the aquaculture industry, the heterotrophic growth characteristics and resultant fatty acid profile of the microalga were studied when cultivated under a variety of controlled salinity and temperature conditions. In addition, the effects of pH on the growth characteristics were also studied. The maximum specific growth rate was affected by initial pH and cultivation temperature, but not by salinity. The optimal pH and temperature ranges for growth were 7.2 to 8.1 and 22.5 to 25.0 °C, respectively. Lipid accumulation and the fatty acid composition were also affected by cultivation temperature and salinity. The optimal temperature range and salinity level for lipid accumulation were 18.0 to 25.0 °C and 11.2 psu, respectively. In all cases the fatty acid distribution was similar, with the most abundant fatty acids being palmitic acid (16:0), palmitoleic acid (16:1 n-7), stearidonic acid (18:4 n-3, SDA), eicosapentaenoic acid (20:5 n-3, EPA), and decosahexaenoic acid (22:6 n-3, DHA). 相似文献
1000.